In U.S. Pat. No. 3,994,764 and the above mentioned copending applications there are disclosed activatable curable adhesive compositions comprising a non-reactive polyurethane polymer or a non-reactive elastomer dissolved in a free radical addition polymerizable methacrylic or acrylic monomer and a free radical addition polymerizable acid monomer co-polymerizable with the methacrylic or acrylic monomer. The solution contains a non-activated free radical polymerization catalyst.
The patent and applications referred to show thermoplastic polyurethane resin and elastomers such as acrylonitrilebutadiene rubbers as the non-reactive polymers, alkyl acrylate and methacrylate esters as the polymerizable acrylic monomers, acrylic and methacrylic acid monomers, with benzoyl peroxide as the catalyst.
As activators there are disclosed dimethylaniline, diethylaniline, N,N-dimethyl-p-toluidine. These may be admixed with an accelerator such as a salt of copper, iron, cobalt manganese or lead, and may be dissolved in a suitable solvent.
Increased heat resistance may be imparted to the adhesive by the addition of a relatively small percentage of a non-reactive epoxy resin.
In one method of use, the activator composition is placed on one mating surface and the adhesive composition is placed on another mating surface. Both surfaces are then brought together and maintained in contact relationship until the adhesive cures to a set.
Alternatively, the activator (and accelerator, if present) may be encapsulated in a microsphere which is insoluble in the adhesive composition. On rupturing the microsphere the adhesive will cure to a set. In one embodiment the adhesive composition is coated on one or both mating surfaces. These are then brought into contact with sufficient pressure to rupture the microspheres. Thereafter, the surfaces are held in contact relationship until the adhesive cures to a set. In another method, the microspheres are ruptured in the adhesive solution which is then applied to at least one of the mating surfaces and both surfaces are thereafter brought into contact. The microsphere-containing adhesive is disclosed in detail in our copending applications Ser. No. 705,333 now U.S. Pat. No. 4,080,238 and Ser. No. 763,145.
While the adhesive compositions and methods for using them are highly satisfactory and give excellent results, care must be used in employing the tertiary amine activators disclosed since these are irritating to the skin and may give toxic reactions.